In modem computer systems, much of their functionality is realized by the ability to network, that is connect, various computers to provide digital communication. Indeed many interconnection schemes have been developed that meet certain needs in various ways. For example, multiprocessor systems can be configured as bus-connected or ring-connected multiprocessor systems. However, the operation and design constraints of such systems do not lead to designs for reliable and scalable switched networks, especially ones that implement crossbar switches employing wormhole routing. The primary limitation of this type of configuration is that ring topologies are not suitable for wormhole-routed switched networks and result in an unacceptably large hop count between end nodes as the number of nodes is scaled.
In another example, the design of bus-oriented interconnection topologies for single-hop communication among multiple transceiver stations is not applicable to scalable switched networks because, among other things, a single-hop interconnection between a large number of nodes is impossible when crossbar switches with a limited number of ports are used. Moreover, such designs use bus-based interconnects which bear little resemblance, if any, to switched interconnects.
Non-bus-oriented single-hop interconnections are also deficient in a number of ways. For example, such configurations suffer the same limitations as described above while also connecting nodes (or switchless networks) directly. This latter feature limits the applicability of the design to end nodes having a large number of ports and to fabrics having zero switches and hence is inapplicable to the design of switched interconnects.
In a traditional approach, ServerNet networks have been designed with two ports, also called colored ports or “X” and “Y” ports, connected to two complete, independent groups of crossbar switches. The interconnection group is complete because every end node interfaces with each group of crossbar switches and each group of switches interfaces with every node. Moreover, the interconnection group is independent because ports of one type are only connected to other ports of the same type. For example, each of the X ports is only connected via an X fabric to other X ports and each of the Y ports in the network are likewise only connected via a Y fabric to other Y ports. Note here that an X fabric is a group of switches that connect all the X ports and only the X ports in the network (similarly for Y ports). In this way, a fabric of one type is designed independently of other fabrics of other types.
A particular concern in network design is fault tolerance. With a large scaled system there is insufficient protection against single points of failure because of the large number of components and it is hard to maintain symmetry because of failed parts. Moreover, scalable topologies (e.g. fat trees) offer design points exponentially far apart. In addition, the relative capacity of an end node shrinks as a network grows in size.
One improved approach has introduced ServerNet Asymmetric Fabrics. With this approach, end nodes are connected using two complete but non-identical groups of switches. However, network expansion requires scalable switched networks. Switched processor-memory subsystems include Sun UE10K, Intel Profusion Chipset, Compaq Alpha EV7. Switched I/O subsystems include ServerNet, NGIO (Next Generation I/O), and Future I/O. However, the issue is scalable yet highly available fabrics. Hence, there is a further need for optimizing the reliability and performance of scalable switched networks.
There exists prior art in the area of bus-connected and ring-connected multi-computer systems, however, the operation and design constraints of such prior art does not lead to designs for reliable and scalable switched networks, especially networks configured for use with crossbar switches employing wormhole routing. Moreover, the prior art does not address how a network comprising multiple incomplete fabrics can simultaneously optimize the reliability and the performance of scalable switched networks.
While the above interconnection schemes provide certain functionality, they are nonetheless limited in at least the ways discussed above. With the advent of network interface cards and other similar devices that provide for multiple ports on one computer system, network design can be expanded beyond the constraints of prior art systems. Importantly, interconnection fabrics need not be constrained to being complete nor colored. Notably, interconnection fabrics can be allowed to be incomplete while allowing for improved fault tolerance while using reduced hardware resources. Toward finding an optimal design, however, there exists a need to determine bounds on various parameters of network designs.